Window sashes are mounted in window frames and the window sashes either slide, rotate or pivot in the window frame between open and closed positions as well as positions therebetween. The windows are opened and closed by various handles and sash bars. However, once the window is closed or is in proximity to the window frame, a locking device is generally provided to lock the sash in the closed position.
A desired arrangement is the use of multipoint locking mechanisms wherein a slider bar is moved to lock keepers on the window sash with a cam roller on the window frame. The advantage of multipoint locking is to provide a secure locking as well as to provide even pressure on the window. Thus, a multipoint locking mechanism tends to prevent warping of the window sash as it maintains flush with the window frame and the weather stripping to assure a good seal. Even if the sash is warped, this multipoint locking mechanism will exert a force on the sash to straighten the sash in the window frame.
It is known in the art to provide multipoint locking wherein the window lock has ramped keepers secured to the window sash and cam rollers on the slider bar which is amounted to the window frame. The slider bar translates up and down on a side wall of the window frame in response to movement of a handle. In placing the handle in the locking position, the cam rollers on the sliding bar each engage a ramped portion of a ramped keeper so as to lock the window sash to the window frame. A problem with the above arrangement is that the window sash must be generally closed for the rollers to engage the ramped keepers.
In order to overcome the above, it has been proposed in U.S. Pat. No. 6,698,970 to utilize an arrangement wherein both the keeper and the cam are wedges which provide increased surface engagement and a greater displacement span.
While the above has been found to be effective, there still exists many windows which use cam rollers and which windows are frequently difficult to lock.